Such an antenna system is described in German Published Patent Application No. 39 10 031. PCT International Published Patent Application No. WO 02/056412, in which two antenna elements are provided for diversity analysis, shows a similar antenna system.
PCT International Published Patent Application No. WO 99/66587 shows an antenna system for diversity operation. The heating conductor field of a vehicle windshield is used, in combination with additional conductor structures not connected to the heating conductor field and located between the heating conductor field and the upper edge of the motor vehicle windshield as an antenna for receiving LMS, UHF, and optionally TV signals.
Antenna systems forming antennas for the LMS and UHF reception from the electrically contacted heating conductor field are known. Filter elements which decouple the vehicle electrical system are needed here for the UHF/TV and LMS reception because of the electrical connections between the antenna connecting point and the heating conductors (see, e.g., European Published Patent Application No. 0 269 723). The heating conductors extend substantially horizontally and substantially parallel to the metallic boundaries of the windshield. The electrical system interference transmitted from the heating current to the heating conductors used as antennas must, as known, be suppressed via modules that have a high resistance using high-frequency technology when the antenna connecting point is electrically connected to the heating conductor field. For UHF/TV reception, there are rod core inductors, which are integrated into the conductor portions supplying the heating current and are usually located in the proximity of the heating current terminals of the heating conductor field.
For LMS reception, this is a current-compensated toroidal core inductor (AM rejection circuit), which is also located in the heating current lead. This AM rejection circuit is a very cost-intensive module, whose own weight (approximately 200 g) results in excessive mechanical loads on both the circuit board and the screw attachment points and is therefore considered highly critical from the point of view of quality assurance. Vibrations occurring under normal driving conditions result in high stresses on the soldered points. In compact vehicles this AM rejection circuit is often installed in the rear trunk lid, so that when the lid is closed, accelerations of approximately 50 g may occur and the entire module may become detached from the screw attachment points.
Antenna systems in composite glass windshields, for example, front windshields of passenger cars, are also known. In this case the antenna wires are located between the two glass panes, which results in increased complexity in contacting. Contacting may often be implemented using so-called flat conductors, which are installed in the composite safety glass pane during the production process. After installing the pane into the vehicle, this flat conductor is then connected to an electronic module.